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HIGH

CVE-2021-23017

CVSS v3

7.7

HIGH

EPSS Score

53.5 %

exploit probability, as of 2026-10-19

CISA KEV

No

known exploited

Exploitation

—

SSVC status

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Affected and fixed versions

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • nginxBitnamifrom 0.6.18 · fixed in 1.20.1and 1 other package
  • nginxAlmaLinux:8all versions · fixed in 1:1.20.1-1.module_el8.5.0+2611+ab304644.almaand 3 other packages
  • nginx-filesystemAlmaLinux:8all versions · fixed in 1:1.20.1-1.module_el8.6.0+2782+a022aca3.almaand 3 other packages

Vendor advisories

  • CVE-2021-23017 Red Hat Product Security403 products fixed · 10 known affected

    nginx: Off-by-one in ngx_resolver_copy() when labels are followed by a pointer to a root domain name

    nginx-all-modules (nginx:1.14) as a component of Red Hat Enterprise Linux 8 · nginx-filesystem (nginx:1.14) as a component of Red Hat Enterprise Linux 8 · nginx-mod-devel (nginx:1.14) as a component of Red Hat Enterprise Linux 8

  • RHSA-2022:0323 Red Hat Product Security55 products fixed

    Red Hat Security Advisory: nginx:1.20 security update

  • RHSA-2021:4618 Red Hat Product Security221 products fixed

    Red Hat Security Advisory: Red Hat Advanced Cluster Management 2.4 images and security updates

  • RHSA-2021:3873 Red Hat Product Security77 products fixed

    Red Hat Security Advisory: Red Hat Advanced Cluster Management 2.2.9 security, bug, and container updates

  • RHSA-2021:3851 Red Hat Product Security10 products fixed

    Red Hat Security Advisory: Red Hat 3scale API Management 2.11.0 Release - Container Images

  • RHSA-2021:3653 Red Hat Product Security1 product fixed

    Red Hat Security Advisory: Red Hat Advanced Cluster Management 2.1.11 security fix and container updates

6 more advisories

Full record on NVD

Description

A security issue in nginx resolver was identified, which might allow an attacker who is able to forge UDP packets from the DNS server to cause 1-byte memory overwrite, resulting in worker process crash or potential other impact.

Technical details

Published
2021-06-01
Exploit-DB
EDB-50973

Frequently asked questions

What is CVE-2021-23017?

A security issue in nginx resolver was identified, which might allow an attacker who is able to forge UDP packets from the DNS server to cause 1-byte memory overwrite, resulting in worker process crash or potential other impact.

Is CVE-2021-23017 actively exploited?

Active exploitation of CVE-2021-23017 has not been confirmed. Its EPSS score was 53.5% on 2026-10-19, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-23017?

CVE-2021-23017 has a CVSS v3 base score of 7.7 (HIGH severity).

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